To understand the mechanisms of Ca absorption in living animals, requires a preparation in which the natural physiological conditions and regulatory mechanisms are not altered and the time course of the movement of the meal through the intestine is preserved. Toward this end we have used an animal model with an intact rat gastrointestinal tract together with tracer methodology, to analyze segmental absorption of Ca from a spontaneously propelled meal. The gastrointestinal tract was removed at various time points between 2 and 360 mins following feeding of a liquid meal containing Ca and divided into seven segments. The data will be analyzed using a compartment model to allow estimation of transit and absorption rate constants, segmental mean residence times maximal absorption rates and the percent of total absorption for Ca. Calcium absorption was studied at three levels of Ca intake; 7.4 mg, 4.0 mg and 8.0mg. The data were analyzed using a compartment model to allow estimation of transit and absorption rate constants, segmental mean rsidence times maximal absorption rates and the of total absorption for Ca. A noncompartmental analysis approach wa also read to estimate mean transit times. The modeling analysis demonstrated only a modest dosage dependency of Ca uptake as a function of Ca feeding levels.